LONDON — British antitrust authorities on Friday accused the pharmaceuticals giant GlaxoSmithKline of paying three rivals to delay the introduction of a generic version of an antidepressant drug. It is the latest so-called pay-for-delay case drawing scrutiny from regulators on both sides of the Atlantic.

The Office of Fair Trading in Britain contended that Glaxo had abused its dominant position in the market, kept prices artificially high and denied “significant cost savings” to Britain’s state-run health provider, the National Health Service.

The British case centers on efforts by three companies, Alpharma, Generics (U.K.) and Norton Healthcare, to market an alternative to Seroxat, GlaxoSmithKline’s brand of paroxetine. The company sells it in the United States under the brand name Paxil.

In recent years, regulators in Europe and the United States have paid greater attention to pay-for-delay deals, suspecting that they may allow pharmaceutical companies to make big profits by exploiting a brief but lucrative period of monopoly over the supply of a product.

“These are blockbuster drugs,” said Farasat Bokhari, a senior lecturer in economics at the University of East Anglia, “so if they are on the market without generics challenging them then companies can maintain high, monopoly profits.

Britain claims GlaxoSmithKline paid three rivals to delay the introduction of a generic version of Seroxat.CreditBogdan Cristel/Reuters

GlaxoSmithKline, according to British authorities, warned the three companies that their generic equivalents would infringe a patent. To resolve the dispute, each of the rivals concluded one or more agreements with GlaxoSmithKline, the Office of Fair Trading said.

“The O.F.T.’s provisional view is that these agreements included substantial payments from GlaxoSmithKline to the generic companies in return for their commitment to delay their plans to supply paroxetine independently,” the regulator said. The agreements with the three companies collectively spanned the years 2001 to 2004, it said.

GlaxoSmithKline said it believed “very strongly” that it had “acted within the law, as the holder of valid patents for paroxetine, in entering the agreements under investigation.”

“These arrangements resulted in other paroxetine products entering the market before GSK’s patents had expired,” the company said. “We have cooperated fully with the Office of Fair Trading in this investigation.”

The company noted that European Union regulators had reviewed the matters covered by the agreements twice and decided to take no action.

The practice of brand-name drug companies paying generic manufacturers to delay selling their copycat versions has also come under scrutiny in the United States, where the Federal Trade Commission has argued that the practice violates antitrust law.

The matter is currently before the United States Supreme Court, which is considering whether a settlement between Solvay Pharmaceuticals, which developed the testosterone treatment AndroGel, and Actavis, which created a generic version, was illegal.

Brand-name and generic drug makers have argued that companies have a right to protect their intellectual property, and that the payments actually saved consumers money by bringing the generic versions to consumers earlier than they normally would have. But the F.T.C. has argued that the opposite is true and that the payments are delaying cheaper versions from entering the market.

The British regulator cited no estimate of the National Health Service’s costs resulting from Glaxo’s supposed deals. But pay-for-delay agreements cost American consumers an estimated $3.5 billion a year, according to the F.T.C. It says that in 2012, the number of “potentially anticompetitive patent dispute settlements” between branded and generic drug companies increased to 40, from 28 in 2011.

Before the period in the British inquiry, Seroxat was one of GlaxoSmithKline’s best-selling drugs and was used to treat, among other conditions, depression and anxiety disorders, the Office of Fair Trading said. Since that time, various generic versions of paroxetine have reached the market.

“The introduction of generic medicines can lead to strong competition on price, which can drive savings for the N.H.S., to the benefit of patients and, ultimately, taxpayers,” said Ann Pope, senior director of services, infrastructure and public markets at the Office of Fair Trading. “It is therefore particularly important that the O.F.T. fully investigates concerns that independent generic entry may have been delayed in this case.”

The action Friday was the first step in formal proceedings: the issuance of a statement of objections. The companies involved can now make written and oral responses.

“No assumption should be made at this stage that there has been an infringement of competition law,” Ms. Pope said. “We will carefully consider the parties’ representations to the statement of objections before deciding whether competition law has in fact been infringed.”

If found to be in breach of antitrust law, a company can in theory be fined up to 10 percent of its worldwide revenue, though penalties rarely are so great.

The European Commission, which is the European Union’s antitrust regulator, said Friday that it had a number of investigations under way within the drug industry and in general was “looking at the so-called pay-for-delay patent agreements.” It added that it had fined AstraZeneca for delaying market entry of generic competitors to its ulcer drug Losec in 2005.

Correction:

An earlier version of this article misstated Solvay Pharmaceutical’s connection to the testosterone treatment AndroGel. Solvay developed AndroGel, but does not sell it. The treatment is sold by Abbott Laboratories.

Katie Thomas contributed reporting from New York.

A version of this article appears in print on , on Page B3 of the New York edition with the headline: Britain Accuses Glaxo Of Paying Rivals for Delay Of Generic Antidepressant. Order Reprints | Today’s Paper | Subscribe